The invention relates to devices and methods for administering substances, including fluid products, for a variety of uses including medical, veterinary, therapeutic, diagnostic, pharmaceutical and/or cosmetic uses. Some preferred examples of administering devices or apparatus comprise injection apparatus, in particular injection pens, and also inhalation apparatus.
In the above-noted uses or applications, it is in most cases important that a very particular product dosage, i.e., a very particular amount of product, is administered. One source of uncertainty in this regard is the possibility that a part of the apparatus which guides the product is not completely filled with the product, but contains air. Without bleeding, the air—or more generally a gas—would be administered together with the product. In the case of subcutaneous administering, for example, while this would not lead to health complications, the correct product dosage would not be administered, but rather a dosage reduced by the air content. In other modes of administering, however, health can additionally be compromised if air is administered together with the product.
Not only can air be present in the product-guiding part of an administering apparatus when product is administered from a reservoir for the first time, but this can also occur, again or for the first time, after administering a prior administration. For instance, a liquid product in an injection cannula can evaporate from the tip of the cannula and dry up the cannula. If, due to the prevailing pressure conditions, a continuing flow of product from the reservoir side is not possible or is not sufficiently rapid, a volume of air forms in the injection cannula from the tip. If product is subsequently administered again, without bleeding beforehand, then the product dosage administered is reduced in accordance with this volume of air.
WO 97/36625, DE 199 00 792 C1 and U.S. Pat. No. 6,228,067 B1 describe administering apparatus which are injection pens which allow the product dosage to be selected. In order to prime the known apparatus, the user presses product through the injection needle of the respective apparatus according to “instinct”, until he has visually confirmed that product is exiting the tip of the needle. Such priming, as bleeding is generally referred to, “by sight” and “instinct” can have the result that an unnecessarily large amount of product is delivered for the purpose of priming and is therefore lost for administering. Moreover, for people with impaired vision, there is an increased risk that the priming process is not correctly performed due to the necessary visual check, which can result in an even greater unnecessary consumption of product or in incomplete bleeding.
In other administering apparatus, for example in inhalation apparatus, it may also be the case—depending on the design—that air cannot be visually monitored in the product-guiding part of the apparatus at all and that it is, therefore, even more difficult to monitor the administering of a particular product dosage.